The present invention relates to a positioning device for preventing an endless belt passed over a plurality of support rollers from being shift to either of opposite sides in the axial direction of the rollers while in operation.
An endless belt is extentsively used with various kinds of machines and apparatuses including image forming apparatuses such as a copier, facsimile apparatus, and a printer. In an image forming apparatus, the endless belt is implemented as a photoconductive belt for carrying a toner image thereon or a transfer belt for transporting a recording medium to which the toner should be transferred. While an endless belt for the above applications is passed over a plurality of support rollers, it is likely that the belt shifts noticeably in the axial direction of the support rollers or weave while in movement. Should the photoconductive belt or the transfer belt, for example, shifts noticeably or weaves as mentioned above, a toner image would not be transferred to an expected position on a recording medium.
To eliminate the above problem, a device for positioning an endless belt has been proposed in various forms in the past. For example, U.S. Pat. No. 2,592,581 teaches a number of annular flanges which are provided on and over the entire length of a support roller and inclined toward the center with respect to the length of the roller. However, the positioning effect achievable with such a flange configuration is limited for the complicated structure. Moreover, because the peripheral surface of such a support roller is not continuous due to the annular flanges, it is not desirable to wrap a belt which should be flat, e.g., a photoconductive belt or a transfer belt around the support roller.